Patent GB-1016981-A (GB)
Title: Improvements in or relating to phase comparison radio navigation systems
Inventor: ROBERTS GRAHAM ESTYN
IPC: G01S1/30
Filed: 1962-07-19
Abstract: 1,016,981. Radio navigation. DECCA Ltd. Oct. 18, 1963 [July 19, 1962], No. 27901/62. Heading H4D. In a receiver for a phase comparison radio navigation system, of the kind in which signals of different but harmonically related frequencies are normally radiated from a master station and two or more spaced slave stations, and in which said normal transmissions from all the stations are periodically interrupted, and signals of these harmonically related frequencies are radiated simultaneously from one station, the plurality of frequencies being radiated from the various stations in sequence in successive interruption periods, and all the radiated signals being locked in phase; means are provided for determining and storing the phase relationship between the effective fundamental frequency signal derived from the multifrequency transmissions from one station during the appropriate interruption period and the normal transmission frequency signal from that station, which signal constitutes one of the frequencies radiated at that time, and for determing the phase relationships between the normal transmissions from the master station and each of the slave stations, wherein each of these latter phase relationships is corrected in accordance with the first mentioned determined and stored phase relationship of the multifrequency transmissions from the appropriate other station. The receiver is used in a CW hyperbolic navigation system wherein the corrections-to the normal phase determinations are used at extreme ranges to overcome phase inaccuracies due to sky wave errors. In the receiver of Fig. 3, the normal transmission from the master station and the purple, green and red slave stations at frequencies of 6f, 5f, 9f and 8f respectively, are received by aerial 10 and fed to tuned amplifiers 12, 13, 14 and 15 where they are separated. The separated signals which may be fed to conventional frequency multipliers and phase discriminators (not shown) are passed to frequency dividers 16, 17, 18 and 19 to produce four signals at frequency 1f. During the interruption of the normal transmissions, the aerial receives the multi-frequency transmission from the appropriate station. The components of the transmission are separated by amplifiers 12, 13, 14 and 15 and frequency divided by dividers 16, 17, 18 and 19, to produce four 1f signals as during the normal transmissions. The components from the amplifiers are also fed to a combiner and pulse former 20, which produces a pulse output at a frequency of 1f, phase locked with the 1f beat signal produced by the combination of the outputs of the amplifiers. The pulse output is fed to four discriminators 25, 26, 27 and 28, for respective phase comparison with the outputs of oscillators 29, 30, 31 and 32. The outputs of the discriminators are fed to control the output phases of the respective oscillators via normally open switches 33, 34, 35 and 36. A switch control 37 detecting the gaps in the normal transmissions closes the switch appropriate to the station transmitting the multi-frequency signal, such that the then controlled oscillator produces a 1f signal locked in phase to the output from pulse former 20, each oscillator being allocated to one of the stations. Twelve signals of frequency 1f are therefore produced, four from oscillators 29, 30, 31 and 32, phase determined by the multi-frequency transmissions from the master, red, green and purple stations respectively and eight from frequency dividers 16, 17, 18 and 19, four of these eight being phase locked to the normal transmissions from the master, purple, green and red slave stations respectively and occurring during the normal transmissions, and the other four being phase locked to the four components of the multi-frequency transmissions, and occurring during the multifrequency transmissions. The twelve 1f signals are fed to a digital phase comparison system as described in Specification 1,016,982, whereby a cyclic sequence of eight different phase comparisons between selected pairs of the 1f signals, is effected. During each multi-frequency transmission the 1f signal from the appropriate oscillator is compared in phase with that from the corresponding divider, and the resulting four multi-frequency phase differences are stored in digital form. During each normal transmission the 1f signal from divider 16, resulting from the transmission from the master station is compared in phase with itself, and then with each of the other three if divider outputs. These last three phase comparison results is corrected three times, firstly by the phase comparison of the normal master transmission with itself to correct for errors in the phase comparing means, secondly by the multifrequency comparison of the master station multi-frequency transmission, and thirdly by the multi-frequency phase comparison of the multi-frequency transmissions from the appropriate slave station.